They arrived in huge numbers on shared bikes after pedaling 30 miles in the evening chill, pumped by the adrenaline of youth and the thrill of embarking on a spontaneous adventure with friends.

The students would emerge on their bikes, in the tens of thousands, seemingly out of nowhere. Like a flash mob on wheels, they rode for hours in the night, by the light of streetlamps, sometimes bursting into verses of the Chinese national anthem.